Large numbers of cataract and lens implant surgical procedures are performed each year, with more than half of these procedures using the extracapsular technique with posterior chamber lens implantation. In this technique, the anterior capsule is partially cut away and the opacified material within the lens capsular bag removed In a growing proportion of these procedures, a posterior chamber intraocular lens is implanted in the ciliary sulcus or in the capsular bag, adjacent the intact posterior capsule. Alternatively, a lens may be implanted in the anterior chamber of the patient's eye. Such implantation may be done concurrently with the cataract extraction or in a later separate procedure.
A problem arising from lens implantation is the difficulty of treating posterior capsule opacification which typically becomes manifest some time after the intraocular lens has been implanted. Although some surgeons have recommended that posterior capsulotomies be performed at the time of the cataract surgery, patients who have had such treatment have suffered a significantly higher incidence of cystoid macular edema as compared to those with capsules left intact at the termination of surgery.
The treatment of posterior capsule opacification after extracapsular surgery is basically of two types, the traditional one being the surgical discising of the posterior capsule, and the more recent involving the use of the Neodymium Yag laser. Although the laser treatment originally showed great promise, there are increasing concerns regarding the safety of the procedure and its effects on the intraocular lens itself. Complications attributed to laser treatment include cystoid macular edema, retinal detachment, lamellar and full thickness macular holes, peripheral retinal tears and hemmorhages, as well as significant lens marking by inadvertently hitting the lens optic or inadvertent cutting of lens haptics with resultant dislocation of the lens. There are also concerns as to liberated free radicals when an intraocular lens or lens haptic is hit with the laser, and recent studies suggest the liberation of cytotoxic agents when the lens optic is hit with the laser.
Because of the above and other concerns as to the safety of the laser treatment, the surgical discission of the posterior capsule is favored by many surgeons. Prior to the present invention, such surgical treatment has been carried out using knives of various types, all of which have shared a common disadvantage in that the configuration of the knife is planar. The approach to the posterior capsule must thus be made by tipping the knife point anteriorly to imbricate the posterior capsule. This cutting motion requires movement by the surgeon of his entire upper arm and elbow in order to incise the capsule. In addition, these knives are very heavy, and if there is minute patient movement, the likelihood of complication is greater.